Thread: Structures? *brain melts*

I was reading the section of the tutorial on structures, and man I'm so lost. Maybe it's because I'm trying to compare structures in C++ to modules in QBasic.

In Qbasic, a module initialized like so:

Code:

: Gosub Module1
:
: Module1:
:    PRINT "This is a module"
:    RETURN

See, to me, I see a structure in C++ as a module... I don't understand it in any other way. In the tutorial, it gives this example:

Code:

struct example
{
      int x;
};
example an_example;  //Treating it like a normal variable type
an_example.x=33;     //How to access it

I was thinking for a while that structures were a sort of "bucket" for a certain specified number of variables. But then, in the last line, where it says "an_example.x=33" why is it doing that? I figure all you would have to do is example.x=33 to set the variable "X" in structure "Example" to a value! Why do they go through the trouble to change the name of example to "an_example" and then change the value of X? It's all so confusing, I'm losing my brain through my ears! Someone help! Thanks!

Well I don't know much of QBasic either lol. I'm in a Intro to Computer Programming class in college, and we just got done learning modules. So, that honestly didn't make any sense. Feel free to try again lol.


My mistake, I shouldn't have brought up Qbasic!

All hail the glory of C++!

Classes are also similar.

Code:

class Example
{
public:
      int x;
};

Example an_example;
an_example.x=33;

Classes are better than structs, although right now I've forgotten why.

Originally posted by bennyandthejets
All hail the glory of C++!

Classes are also similar.

Code:

class Example
{
public:
      int x;
};

Example an_example;
an_example.x=33;

Classes are better than structs, although right now I've forgotten why.

Sorry... I didn't catch your point.

I just wanna know why it changes "example" to "an_example"

And perhaps an example of how a structure would be used to get a certain result or something, that might help out too! Thanks for working with me this far! lol...

Originally posted by Bubba

Code:

class Example
{
public:
      int x;
};

Example an_example;
an_example.x=33;

should be

Code:

class Example
{
  public:
   Example (void) {}: 
   int x;
};

Example *an_example=new Example();
an_example->x=33;

Care to explain yourself?

Originally posted by bennyandthejets
Care to explain yourself?

Thank you! Man... I don't even know where this is going! lol... I just wanna know what the structure is doing in each action it takes.

Bubba, you forgot 'delete an_example;'

Anyways, when you have something like that, 'example' is essentially its own data type. Its a template, if you will.

For example, you don't say:
int = 1;
You first create an instance of an integer, and then set it equal to 1.
int x = 1;

In the same way, 'example' is a type, and you need to create an instace of it:
example an_example;
...or dynamically...
example* an_example = new example;
... do some stuff, and free the memory ...
delete an_example;

(Note: the first method is recommended unless there is a reason you are dynamically allocating it, which I'm guessing you haven't gotten to yet.)

Classes/structs allow you to group data which has something in common. For example, here is the traditional Cat class:

Code:

class Cat
{
public:
      int Age;
      int Weight;
      void Meow();
      void Sleep();
};

You group all the things related to Cats in one object. But, what if you have two cats?

Code:

Cat Tintin;
Cat Chelsea;

(Those are the names of my cats)
Those statements create two objects based on the type 'Cat'. Ie, both objects have Age and Weight, and they can both Meow() and Sleep(). You cannot do this:

Code:

Cat.Age=5;

Because Cat is not an object, it is a type. Therefore, there is actually no variable in memory which can be assigned the value '5'.